The present invention relates generally to a giant magnetoresistive read sensor for use in a magnetic read head. In particular, the present invention relates to a giant magnetoresistive read sensor having an enhanced giant magnetoresistive response and an increased exchange pinning field strength.
Giant magnetoresistive (GMR) read sensors are used in magnetic data storage and retrieval systems to detect magnetically-encoded information stored on a magnetic data storage medium such as a magnetic disc. A time-dependent magnetic field from a magnetic medium directly modulates the resistivity of the GMR read sensor. A change in resistance of the GMR read sensor can be detected by passing a sense current through the GMR read sensor and measuring the voltage across the GMR read sensor. The resulting signal can be used to recover encoded information from the magnetic medium.
A typical GMR read sensor configuration is the GMR spin valve, in which the GMR read sensor is a multi-layered structure formed of a nonmagnetic spacer layer positioned between a ferromagnetic pinned layer and a ferromagnetic free layer. The magnetization of the pinned layer is fixed in a predetermined direction, typically normal to an air bearing surface of the GMR spin valve, while the magnetization of the free layer rotates freely in response to an external magnetic field. The resistance of the GMR spin valve varies as a function of an angle formed between the magnetization direction of the free layer and the magnetization direction of the pinned layer. This multi-layered spin valve configuration allows for a more pronounced magnetoresistive effect, i.e. greater sensitivity and higher total change in resistance, than is possible with anisotropic magnetoresistive (AMR) read sensors, which generally consist of a single ferromagnetic layer.
A pinning layer is typically exchange coupled to the pinned layer to fix the magnetization of the pinned layer in a predetermined direction. The pinning layer is typically formed of an antiferromagnetic material. In antiferromagnetic materials, the magnetic moments of adjacent atoms point in opposite directions and, thus, there is no net magnetic moment in the material.
A seed layer is typically used to promote the texture and enhance the grain growth of each of the layers consequently grown on top of it. The seed layer material is chosen such that its atomic structure, or arrangement, corresponds with the preferred crystallographic and magnetic orientations of the GMR spin valve. The seed layer is typically formed of nonmagnetic materials such as tantalum (Ta) or zirconium (Zr).
The overall response of a GMR spin valve, or its magnetoresistive effect, directly depends upon the GMR ratio (the maximum absolute change in resistance of the GMR spin valve divided by the resistance of the GMR spin valve multiplied by 100%) of the spin valve. The overall response of the GMR spin valve also depends upon strength of the exchange pinning field that exists between the pinning layer and the pinned layer. By increasing both the GMR ratio and the strength of the exchange pinning field between the pinning and pinned layers, the GMR spin valve will be capable of an increased read sensitivity and stability, thereby allowing for use in storage mediums with greater storage densities.
Achievement of the preferred crystallographic and magnetic orientations of each of the layers in the GMR spin valve increases both the GMR ratio and the strength of the exchange pinning field between the pinned and pinning layers. Accordingly, there is a need for a seed layer material that enhances the GMR response by promoting the preferred crystallographic and magnetic orientations of each of the layers in the GMR spin valve.